CN112723494B

CN112723494B - Water treatment technology for promoting synchronous removal of refractory organic matters and nitrogen elements by electro-activated persulfate

Info

Publication number: CN112723494B
Application number: CN202110067753.4A
Authority: CN
Inventors: 林辉; 彭晗君
Original assignee: Dongguan University of Technology
Current assignee: Dongguan University of Technology
Priority date: 2021-01-19
Filing date: 2021-01-19
Publication date: 2022-09-13
Anticipated expiration: 2041-01-19
Also published as: CN112723494A

Abstract

The invention discloses a water treatment technology for promoting the synchronous removal of refractory organics and nitrogen elements by electro-activating persulfate, which develops a new water treatment technology by utilizing the characteristics of active free radicals and hydrogen ions generated by the electro-activation of the persulfate, and can realize the efficient synchronous removal of the refractory organics and the nitrogen elements in water. The invention constructs an electrochemical water treatment system in a circulating filtration flow mode by taking a bifunctional electro-catalytic membrane capable of efficiently activating persulfate and catalyzing reduction of nitrate and an electro-activated persulfate technology as a core, and obtains satisfactory effect when being applied to the deep treatment of actual industrial sewage. The invention combines the capabilities of oxidizing and degrading organic matters and reducing and removing nitrates of an electrochemical system, further expands the application range of the electrochemical water treatment technology, and provides a new direction for the development of the electrochemical water treatment technology.

Description

Water treatment technology for promoting synchronous removal of refractory organic matters and nitrogen elements by using electroactive persulfate

Technical Field

The invention relates to the field of electrochemical water treatment technology, in particular to a water treatment technology for promoting synchronous removal of refractory organic matters and nitrogen elements by using electroactive persulfate.

Background

In municipal sewage and most industrial sewage, the sewage contains two pollutants of organic matters and nitrogen elements. The existing form of inorganic nitrogen element in water body is mainly ionic state, including nitrate radical, nitrite radical and ammonia radical, in which the nitrite radical is instable and can be easily oxidized into nitrate radical. Aiming at the problem that organic matters and ammonia nitrogen in sewage can be synchronously removed by adopting an advanced oxidation method, but the nitrate nitrogen in the highest valence state cannot be removed by adopting the advanced oxidation method.

Currently, the only methods for synchronously removing organic matters and total nitrogen in water are biological methods, such as a typical A/O, A/A/O process in an activated sludge process, an oxidation ditch process and the like. The biological method utilizes the growth metabolism of microorganisms, and the nitrification firstly converts ammonia nitrogen into nitrate nitrogen through the nitrification-denitrification process, and then converts the nitrate nitrogen into nitrogen through denitrification, so as to realize the removal of nitrogen elements in the water body. The biological method has mature process conditions, simple and convenient equipment operation and maintenance and ideal treatment effect; but the efficiency is not high, the hydraulic retention time is long, the structure volume is large, the occupied area is wide, certain requirements are met on water quality conditions, the carbon-nitrogen ratio needs to be regulated, a carbon source needs to be added for sewage with low organic matter concentration, and resource waste is easily caused. Biological methods have been widely used in municipal sewage treatment plants in China. Industrial sewage is difficult to directly treat by a biological method because of large water quality difference, large water quantity change and relatively high water outlet temperature, and needs to be pretreated firstly. Moreover, the microbial denitrification process is a metabolic process which needs to consume organic matters, and industrial sewage often contains refractory organic matters which are difficult to utilize by high-concentration microbes, so that the phenomenon that the nitrate concentration in the effluent of secondary biochemical treatment of the industrial sewage is high and does not meet the discharge standard is caused. The ion exchange method, electrodialysis, reverse osmosis or catalytic reduction and other technologies can be used as advanced treatment technologies to further reduce the nitrate in the secondary biochemical effluent of the industrial sewage, so that the secondary biochemical effluent reaches the discharge standard. The membrane separation advanced treatment processes such as electrodialysis, reverse osmosis and the like have high nitrate removal efficiency and good effect, but have the problems of high cost and difficulty in treating concentrated water generated in the filtering process. On the other hand, these techniques only achieve concentration and transfer of nitrate, and cannot fundamentally solve the problem of nitrate pollution. The catalytic reduction technology can realize the reduction and conversion of nitrate into nitrogen or ammonia nitrogen with lower valence state, and thoroughly realize the reduction and removal of nitrate.

In recent years, water treatment technology for electrochemical catalytic reduction of nitrate has been widely studied by scholars at home and abroad. Compared with other catalytic reduction technologies, the electrocatalytic reduction technology has the advantages of mild action conditions, strong controllability, easy realization of automatic management and great potential in practical popularization and application. It is noted that in the electrochemical treatment system, the anode has the capacity of oxidizing and degrading organic matters and ammonia nitrogen, and the cathode has the capacity of reducing and removing nitrate. Therefore, the electrochemical water treatment technology is expected to replace a microbiological method to become a next-generation water treatment technology method for synchronously removing organic matters and total nitrogen.

In order to improve the oxidative degradation efficiency of refractory organic matters in an electrochemical system, researchers introduce free radical reaction in the electrochemical system and develop a series of novel electrochemical water treatment technologies represented by electro-Fenton, electro-activated persulfate and the like. It was found that the process of persulfate electroactive occurs at the cathode and the sulfate radicals generated are easily combined with water molecules and converted into hydroxyl radicals and hydrogen ions, while the reduction process of nitrate is a process consuming hydrogen and the reduction of nitrate also occurs at the cathode. The invention takes the membrane as an entry point, takes a bifunctional electrocatalytic membrane capable of efficiently activating persulfate and catalyzing nitrate reduction as a core, and constructs an electrochemical system capable of synchronously promoting organic matter degradation and nitrogen element removal. In the system, persulfate is activated at a cathode to generate sulfate radicals, hydroxyl radicals and hydrogen ions, wherein the sulfate radicals and the hydroxyl radicals can promote the oxidative degradation of organic matters and ammonia nitrogen, and the hydrogen ions can promote the reduction of nitrate, so that the degradation of the organic matters and the removal of nitrogen elements in sewage are synchronously promoted.

Disclosure of Invention

In view of the above, the present invention provides a water treatment technology for promoting the synchronous removal of refractory organics and nitrogen elements by using an electroactive persulfate, which is a bifunctional electrocatalytic membrane capable of efficiently activating persulfate and catalyzing the reduction of nitrate, and an electroactive persulfate technology as a core, and can realize the synchronous removal of organics and nitrogen elements in a non-biological system, so as to solve the problems of long hydraulic retention time, low treatment efficiency, wide occupied area of structures, etc. of biological denitrification, and provide a new direction for the application research of persulfate in water treatment.

In order to achieve the purpose, the invention adopts the following technical scheme:

a water treatment technology for promoting the synchronous removal of refractory organics and nitrogen element by using electrically activated persulfate features that an electrolytic system with circulating filtering flow is constructed, which is arranged in order from cathode to anode and at a certain distance from cathode to anode, and Ti/TiO is used as cathode material ₂ -NTA/Cu-Co bifunctional electrocatalytic membrane, the bifunctional electrocatalytic membrane being made of TiO ₂ NTA as an intermediate layer, TiO ₂ in-NTAThe surface of the interlayer is densely covered with recessed nanotube array, TiO ₂ Forming the surface of the Cu and Co transition metal ion catalytic layer by pulse constant current electrodeposition through the NTA intermediate layer, wherein Cu and Co metal ions are simultaneously loaded on the inner wall surface of the nanotube; the anode material adopts a mesh ruthenium iridium electrode, the cathode and the anode are respectively connected with the cathode and the anode of a direct current stabilized power supply through leads, the electrolysis is carried out in a constant current mode, and the current density adopts 20-40mA/cm ² And a peristaltic pump is used as a driving force for water circulation of the electrolytic system, the peristaltic pump is set to rotate at a speed of 20-50r/min, persulfate is added to promote oxidative degradation of refractory organic matters, and the pH value of the electrolytic system is controlled to be 5-8.

Compared with the prior art, the invention has obvious advantages and beneficial effects, and concretely, the technical scheme shows that the invention takes a bifunctional electrocatalytic membrane capable of efficiently activating persulfate and catalyzing nitrate reduction and an electroactive persulfate technology as the core, develops an electrochemical water treatment technology capable of synchronously promoting organic matter degradation and nitrogen element removal, can realize synchronous removal of organic matter and nitrogen element in a non-biological system, solves the problems of long hydraulic retention time, low treatment efficiency, wide occupied area of structures and the like of biological denitrification, and provides a new direction for application research of persulfate in water treatment.

Compared with the traditional electrochemical water treatment technology, the method has the greatest advantage of skillfully combining the oxidation and reduction capabilities of an electrochemical system. By applying the difunctional electrocatalytic membrane capable of activating persulfate and promoting nitrate reduction in an electrochemical system, the invention can efficiently activate persulfate at a cathode, generate hydroxyl free radicals and sulfate free radicals with strong oxidizing capability, effectively improve the degradation rate of organic matters in sewage, and simultaneously realize the catalytic reduction of nitrate at the cathode, thereby achieving the purpose of synchronously removing the organic matters and the nitrate in the sewage. The invention is applied to the actual sewage treatment containing nitrate, under the conditions that the COD concentration of inlet water is 286 +/-22 mg/L, the nitrate concentration is 192 +/-18 mg/L and the dosage of PDS is 10 +/-5 mmol/L, the electrolysis is carried out for 120 +/-30 min, the COD concentration of outlet water is reduced to 32 +/-5 mg/L, the nitrate concentration is reduced to 7 +/-5 mg/L and the PDS concentration is reduced to 0 mmol/L. The COD removal rate is about 89.6%, the nitrate removal rate is about 96.1%, and the PDS is completely activated.

In order to more clearly illustrate the structural features and effects of the present invention, the present invention will be described in detail with reference to the accompanying drawings and specific embodiments.

Drawings

FIG. 1 is a schematic diagram of an electrochemical system in a continuous flow filtration mode in accordance with an embodiment of the present invention.

FIG. 2 shows Ti/TiO compounds in accordance with an embodiment of the present invention ₂ Schematic diagram of NTA/Cu-Co bifunctional electrocatalytic membrane.

FIG. 3 shows the residual ratio of COD in example 4 of the present invention.

FIG. 4 shows the residual ratio of nitrate in example 4 of the present invention.

FIG. 5 shows the residual COD rates of different PDS dosing regimes in example 5 of the present invention.

FIG. 6 shows the residual nitrate ratios for different PDS dosing regimes in example 5 of the present invention.

The attached drawings indicate the following:

1. cathode 101, TiO ₂ -NTA intermediate layer

102. Nanotube array 103, Cu, Co transition metal ions

2. Anode 3, DC regulated power supply

4. A peristaltic pump.

Detailed Description

The invention relates to a water treatment technology for promoting the synchronous removal of refractory organic matters and nitrogen elements by using electroactive persulfate, which adopts an electrolytic system in an anode-cathode-anode three-electrode circulating filtration flow mode, and a figure 1 shows a specific structure of an electrochemical system in a continuous flow filtration mode, and is applied to the electrolytic treatment of industrial sewage.

The electrolytic system is arranged in a cathode-anode-cathode sequence at a certain distance, and the cathode 1 is made of Ti/TiO with the diameter of 30mm, the aperture of 20 mu m and the thickness of 2mm ₂ The anode 2 is made of 30mm diameter and 1mm thickness mesh ruthenium iridium electrode, the cathode 1 and the anode 2 are divided intoRespectively connected with the cathode and the anode of a DC stabilized power supply 3 through leads, and electrolyzed in a constant current mode with the current density of 20-40mA/cm ² (ii) a The electrolytic system adopts a peristaltic pump 4 as the driving force for water circulation of the electrolytic system, and preferably, the set rotating speed of the peristaltic pump is 20-50 r/min. The electrolytic system promotes the oxidative degradation of the refractory organic matters by adding persulfate, and the pH value of the electrolytic system is controlled to be between 5 and 8.

Wherein, as shown in FIG. 2, the cathode 1 is Ti/TiO system ₂ the-NTA/Cu-Co bifunctional electrocatalytic membrane has TiO ₂ NTA intermediate layer 101, TiO ₂ -nanotube array with densely-spaced depressions 102, TiO in the surface of the NTA intermediate layer ₂ And forming the surface of the Cu and Co transition metal ion 103 catalytic layer by pulse constant-current electrodeposition of the NTA intermediate layer, wherein the Cu and Co metal ions are simultaneously loaded on the inner wall surface of the nanotube. Compared with the traditional electrochemical cathode material, the invention has the greatest advantage that the two functions of persulfate activation and nitrate catalytic reduction can be simultaneously realized.

The Ti/TiO ₂ the-NTA/Cu-Co bifunctional electrocatalytic membrane is prepared by a specific process, and comprises the following specific steps: step 1, material taking: taking a piece of porous titanium base material; step 2, high-pressure electrolysis: carrying out ultrasonic cleaning on the porous titanium substrate and then drying; the porous titanium substrate is used as an anode, and a Pt sheet is used as a cathode to be electrolyzed for 2-4 times in the configured electrolyte at high pressure, and each time of electrolysis is 30-60 min; after the electrolysis is finished, taking out the electrode slice, cleaning and drying; step 3, annealing: annealing for 1-3 h at 450-550 ℃ in a muffle furnace, naturally cooling to room temperature, taking out, cleaning and drying to obtain TiO ₂ Intermediate layer of NTA, TiO ₂ -the surface of the NTA intermediate layer is densely populated with an array of recessed nanotubes; step 4, electrochemical deposition: TiO prepared by the above method ₂ Ti/TiO of the intermediate layer of NTA ₂ And (3) taking an NTA electrode as a cathode, taking an ultrasonically cleaned and dried porous titanium substrate as an anode, placing the anode in the prepared electrodeposition liquid containing Cu and Co transition metal ions, performing pulse constant-current electrodeposition for 1-3 times, wherein each time is 10-20 min, and after the electrodeposition is finished, taking out the electrode, cleaning and drying to prepare the bifunctional electrocatalysis membrane capable of efficiently activating persulfate and catalyzing nitrate reduction.

Wherein, in the step 1, the porous titanium substrate is preferably a titanium sheet with the pore diameter of 10-20 μm, the diameter of 20-50mm and the thickness of 1-2 mm. The porous titanium substrate is a novel structural and functional material, which can effectively exert mechanical properties and structural properties under light weight. Compared with a solid non-porous material, the porous titanium integrates the characteristics of titanium metal and a porous material, can reduce the amount of the material without weakening the strength, simultaneously keeps high toughness and corrosion resistance, and particularly has a porous structure which can effectively improve the specific surface area.

In the step 2, the method for drying the porous titanium substrate after ultrasonic cleaning preferably comprises the steps of grinding the surface of the porous titanium substrate by using 100-mesh sand paper, ultrasonically cleaning the porous titanium substrate for 10min by sequentially using acetone, absolute ethyl alcohol and deionized water, repeating the steps twice, placing the cleaned porous titanium substrate in an electrothermal blowing drying oven, and drying the substrate at 55 ℃ to ensure the cleanness of the porous titanium substrate. And, in step 2, the electrolyte solution is preferably prepared with the following components: 97-98.5% of glycol solution, 1.25-2.75% of deionized water and 0.15-0.25% of sodium fluoride or ammonium fluoride by weight ratio, wherein the properties of the electrolyte have important influence on the oxidation of Ti and the dissolution process of TiO2, and the electrolyte is one of main influence factors for determining the morphology of the TiO2 nanotube. It has been shown that organic electrolytic solutions containing fluoride ions are the more efficient type of electrolyte. The content of fluorine ions and water in the organic electrolyte is one of the factors influencing the electrolysis efficiency of TiO 2. If the water content in the electrolyte is too high, hydrogen evolution and oxygen evolution reactions can occur, and the efficiency of Ti oxidation reaction is greatly reduced. Fluoride ion is one of the reactants participating in the dissolution of TiO2, and if the fluoride ion concentration is too high, TiO2 dissolves too quickly to form a regular tubular structure. In particular, in the step 2, a direct-current stabilized power supply is adopted for high-voltage electrolysis, and the voltage is 50-70V. While the traditional electrolysis adopts low pressure, generally 3-20V, the electrolysis efficiency can be increased by adopting high-pressure electrolysis, and the electrolysis time can be shortened from the traditional more than 3 hours to 30-60 minutes. Furthermore, in the high-pressure electrolysis in step 2, it is preferable that two pieces of Pt sheet electrodes of 30mm × 0.1mm are used as cathodes, a porous titanium substrate cleaned and dried in advance is used as an anode, the three pieces are placed in an electrolytic cell at an equal interval of 1.5 cm, a dc regulated power supply is used as a power supply, a constant voltage of 60V is set, a current is set to a maximum value, and constant-voltage electrolysis is performed for 1 hour to achieve anodic oxidation of the porous titanium substrate.

In the step 4, the electrodeposition solution containing transition metal ions of Cu and Co is prepared by a preferable method, wherein a certain weight part of copper sulfate pentahydrate and cobalt sulfate heptahydrate are respectively weighed, a proper weight part of deionized water is weighed, the copper sulfate pentahydrate and the cobalt sulfate heptahydrate are combined and transferred into a beaker, the three are ultrasonically mixed for 10min, and the pH value is adjusted to 4.0 by using 10% concentrated sulfuric acid, so as to prepare the electrodeposition solution, wherein the copper sulfate pentahydrate is 1 part, the cobalt sulfate heptahydrate is 1 part, and the deionized water is 100 parts by weight. The specific gravity of Cu and Co transition metal ions is not too much or too little, the loading is small when the specific gravity is too little, and the covered particles are too large when the specific gravity is too much, so that the specific surface area is reduced, the active potential is low, and the electrocatalytic effect is not good.

In step 4, the electrochemical deposition preferably adopts an electrochemical workstation timing constant potential mode to realize pulse constant current electrodeposition, pulse current output can be realized by adjusting working parameters of cathode current, anode current, cathode time, anode time, data recording interval and cycle number, and the operating parameters of the pulse constant current electrodeposition are as follows: the average current density was 15mA/cm ² Pulse frequency is 50Hz, duty ratio is 40%, and deposition time is 10 min. Preferably, the present invention simply implements pulse constant current electrodeposition using a Chronopotentiometry (CP) mode in the shanghai huachi 660e electrochemical workstation.

The bifunctional electrocatalytic membrane takes a porous titanium sheet as a base material and prepares TiO by in-situ anodic oxidation ₂ -NTA intermediate layer (also known as TiO) ₂ Nanotube array intermediate layer) and loading Cu and Co metal ions on the surface by an electrodeposition method. The titanium electrode has stable performance, long service life and good corrosion resistance. TiO2 ₂ The nanotube array being TiO ₂ In a form of TiO, in this form ₂ Has large specific surface area and high aspect ratio. Introduction of TiO ₂ The titanium electrode in the middle layer of the nanotube array can load more metal ions under the same area, so that more active sites are provided for electrochemical catalytic reaction. The function of the electrocatalytic film depends on the type of metal ion depositedFor example, Cu and Co ions have good effects on the electrocatalytic reduction of nitrate and the electrocatalytic activation of persulfate, and the invention can simultaneously realize the high-efficiency electrocatalytic activation of persulfate and the electrocatalytic reduction of nitrate by introducing Cu and Co metal elements on the surface of an electrode. And two kinds of metal ions are introduced to the surface of the electrocatalytic membrane simultaneously, so that the effect that one is added and the other is larger than two can be achieved. In other words, the electrocatalytic membrane simultaneously loaded with Cu and Co metal ions has better effects of activating persulfate and catalyzing the reduction of nitrate than the electrocatalytic membrane loaded with single metal.

The system of the invention adopts the peristaltic pump as the driving force of the water circulation of the electrolytic system, and the set rotating speed of the peristaltic pump is 20-50 r/min. The selection data of the rotating speed is 20-50r/min because if the rotating speed is too low, the water flow speed is too low, nano bubbles generated in the electrolytic process are easy to accumulate on the surface of an electrode, the electrolytic effect is influenced, in addition, the voltage is caused to change violently, and the reaction system is instable. On the contrary, if the rotating speed is too high, the flow velocity is too fast, the impact force of water flow is large, the stability of the catalyst layer of the electro-catalytic membrane is adversely affected, and the flow velocity is too fast, the water flow shearing force on the surface of the electrode is too large, so that the reactant is not favorably combined with the active sites, and the treatment effect is affected.

Preferably, the invention adopts a constant current mode to carry out electrolysis, and the current density adopts 20-40mA/cm ² . If the current density is too low, the electrode potential does not reach the oxidation reaction potential barrier of organic matters and ammonia nitrogen or the reduction reaction potential barrier of nitrate and nitrite, and no reaction occurs. However, if the current density is too high, the electrode potential will greatly exceed the required reaction barrier, resulting in a waste of energy.

In addition, in the invention, the persulfate in the electrochemical system can be added in a single time or in multiple times, and in the practical engineering application, the concentration of the persulfate in the water body can be directly controlled by the administration system. The amount of persulfate to be added depends mainly on the specific water quality conditions. Because the introduction of an insufficient amount of persulfate into the electrochemical system reduces the efficiency of the reaction, prolongs the reaction time, and results in incomplete removal of organics and total nitrogen. And excessive persulfate is introduced, so that self-quenching reaction occurs between sulfate radicals, the utilization rate of persulfate is reduced, resource waste is caused, and meanwhile, the cost of water treatment is greatly increased due to the large use of persulfate. The adding amount of the persulfate is determined by the concentration of the refractory organic matters in the sewage and the concentration of the nitrate together. The dosage of persulfate is determined according to the dosage of sulfate free radicals and hydroxyl free radicals required by complete mineralization of the refractory organic pollutants. And determining the addition amount of another persulfate according to the maximum value of hydrogen atoms required by the reduction of the nitrate and the pH change caused by the difference of hydrogen ions generated in the activation process of the persulfate. The pH value of the electrochemical system is generally required to be between 5 and 8, and the peracid or over-alkali environment is not favorable for the electrochemical redox reaction. And comparing the two values to obtain a persulfate adding amount value, and taking the smaller value. In the actual operation process, the calculation method is only used as a reference, and the specific adding amount can be determined through preliminary experiments. The determination of the dosing mode depends mainly on the amount of persulfate used and the rate of activation of persulfate, and also requires case-specific analysis. In general, the rate of persulfate activation is a fixed value for a given set of electrolysis conditions, but it is not excluded that variations in water quality will affect the rate of persulfate activation. When the usage amount of persulfate is small and the activation time is close to the reaction time, a single-adding mode can be adopted; when the consumption of the persulfate is large or the activation time is far shorter than the reaction time, a multi-time adding mode is considered, the generation of sulfate radical free radical self-quenching reaction caused by one-time adding of a large amount of persulfate is avoided, and the utilization rate and the reaction rate of the persulfate can be effectively improved.

The mechanism of promoting the degradation of nitrate by persulfate is as follows: persulfate obtains electrons at active sites on the surface of the electrode to break bonds for cracking (reactions 1 and 2), sulfate radicals generated by persulfate activation further react with water molecules to generate hydroxyl radicals, sulfate ions and hydrogen ions (reaction 3), and the hydrogen ions promote the reduction of the nitrate ions on the surface of the electrode.

HSO ₅ ^— + e ^— →SO ₄ ^·— +OH ^— / HSO ₅ ^— + e ^— →SO ₄ ^2— + HO (reaction 1)

S ₂ O ₈ ^2— +e ^— →SO ₄ ^2— +SO ₄ ^·— (reaction 2)

SO ₄ ^·— +H ₂ O→HO·+H ⁺ +SO ₄ ^2— (reaction 3)

NO ₃ ^— +2H ⁺ +2e ^— →NO ₂ ^— +H ₂ O (reaction 4)

2NO ₃ ^— + 12H ⁺ + 10e ^— →N ₂ +6H ₂ O (reaction 5)

NO ₃ ^— +10H ⁺ +8e ^— →NH ₄ ⁺ + 3H ₂ O (reaction 6)

According to the invention, persulfate is introduced into the electrochemical filtration system in the continuous flow mode to promote oxidative degradation of the organic matters difficult to degrade. The mechanism of promoting the degradation of organic matters by the persulfate is as follows: hydroxyl free radicals and sulfate free radicals can be generated in the persulfate activation process, and the free radicals have strong oxidizing property and can perform chain reaction with organic matters without selectivity so as to thoroughly mineralize the organic matters. The specific description is as follows:

SO ₄ ^·— +M→M ^· +SO ₄ ^2— + degradation products (reaction 7)

HO·+M→M ^· +OH ^— + degradation products (reaction 8)

M ^· +S ₂ O ₈ ^2— → SO ₄ ^·— +SO ₄ ^2— + degradation products (reaction 9)

M ^· +H ₂ O→HO·+SO ₄ ^2— + degradation products (reaction 10)

Further, the persulfate is peroxymonosulfate or peroxydisulfate, where acting is hydrogen persulfate (HSO) ₅ ^— ) Or persulfate (S) ₂ O ₈ ^2— ) Thus, potassium monopersulfate complex salts and/or potassium peroxodisulfate, sodium peroxodisulfate, ammonium peroxodisulfate, etc. contain or are capable of hydrolyzing in water to produce hydrogen persulfate (HSO) ₅ ^— ) Or persulfate (S) ₂ O ₈ ^2— ) Salts can be used in the present invention.

To better illustrate the application effect of the present invention, the following 5 preferred embodiments are described in detail with reference to the accompanying drawings.

Examples electrolysis experiments of actual industrial wastewater were conducted using an electrolysis system in an anode-cathode-anode three-electrode circulating filtration flow mode. In this example, the anode is a mesh ruthenium iridium electrode with a thickness of 1 mm. Before the actual industrial sewage degradation experiment is carried out, the device is firstly used at 40mA/cm ² Electrolyzing the high-concentration sodium sulfate solution for 20-30min at the current density of (1), and repeating twice to activate the electrode and stabilize the electrode performance. The main water quality index parameters of the actual industrial sewage treated by the method are shown in the table 1. Before the electrolytic treatment, the actual industrial sewage is subjected to vacuum filtration by using a water system filter membrane with the pore diameter of 0.22 mu m, so that the phenomenon of water flux reduction caused by the blockage of a porous electrode by larger particles is prevented.

TABLE 1 Secondary Biochemical effluent quality index of landfill leachate

Index of water quality

pH

TOC

COD

NH ₄ ⁺ -N

NO ₃ ^- -N

Electrical conductivity of

Unit

/

mg/L

mS/cm ²

Water quality parameter

6~8

110~118

286~308

1.2~1.9

43.4~47.4

4.5~5

Example 1

Example 1 consists in exploring the effect of the peristaltic pump speed setting on the actual industrial wastewater treatment effect.

The embodiment adopts 60mL of actual industrial wastewater as an electrolysis system, the rotating speeds of the peristaltic pumps are respectively set to be 10, 30, 60 and 100r/min, and the current density is set to be 20mA/cm ² The amount of PDS added was set at 10mM, respectivelyAnd (3) performing electrolysis for 0, 5, 10, 20, 30, 60, 90 and 120min, and performing sampling analysis, wherein the detected water quality indexes comprise PDS concentration, COD concentration and nitrate concentration. The results of the experiment are shown in table 2.

TABLE 2 influence of the rotational speed of the peristaltic pump on the actual industrial wastewater treatment effect

Peristaltic pump speed (r/min)	10	30	60	100
					PDS residual ratio (%)	0	0	10	45
COD removal Rate (%)	70.3	89	48	27
					Nitrate removal Rate (%)	77	96.1	51	32

As can be seen from Table 2, when the rotation speed of the peristaltic pump is 30r/min, the PDS residual rate is zero, the COD removal rate is 89%, the nitrate removal rate is 96.1%, and the sewage treatment effect is optimal.

Example 2

Example 2 consists in exploring the effect of current density settings on the actual industrial wastewater treatment effect.

The embodiment adopts an electrolytic system of 60mL of actual industrial wastewater, the rotating speed of the peristaltic pump is respectively set to be 30r/min, and the current density is set to be 10, 20, 30 and 40mA/cm ² The dosage of PDS is set to 10mM, samples are respectively analyzed in electrolysis for 0, 5, 10, 20, 30, 60, 90 and 120min, and the detected water quality indexes comprise PDS concentration, COD concentration and nitrate concentration. The results are shown in Table 3.

TABLE 3 influence of Current Density on the actual Industrial wastewater treatment Effect

Current Density (mA/cm) ² ）	10	20	30	40
					PDS residual (%)	8	0	0	0
COD removal Rate (%)	63	89	90	92
					Nitrate removal rate (%)	72	96.1	96.7	96.9

As can be seen from Table 3, when the current density was 40mA/cm ² When the wastewater treatment system is used, the PDS residual rate is zero, the COD removal rate is 92%, the nitrate removal rate is 96.9%, and the wastewater treatment effect is optimal.

Example 3

Example 3 was conducted to investigate the effect of persulfate addition on the treatment effect of actual industrial wastewater.

The embodiment adopts an electrolytic system of 60mL of actual industrial wastewater, the rotating speeds of peristaltic pumps are respectively set to be 30r/min, and the current density is set to be 20mA/cm ² The dosage of PDS is set to be 5, 10, 20 and 30mM respectively, samples are taken for analysis at 0, 5, 10, 20, 30, 60, 90 and 120min of electrolysis respectively, and the detected water quality indexes comprise PDS concentration, COD concentration and nitrate concentration. The results of the experiment are shown in table 4.

TABLE 4 influence of PDS dosage on the actual Industrial wastewater treatment Effect

PDS dosage (mM)	5	10	20	30
					PDS residual (%)	0	0	9	33
COD removal Rate (%)	69	89	86	82
					Nitrate removal rate (%)	82	96.1	91	90

As can be seen from Table 4, when the amount of PDS added was 10mM, the residual PDS rate was zero, the COD removal rate was 89%, the nitrate removal rate was 96.1%, and the effect of sewage treatment was the most desirable.

Example 4

Example 4 is to investigate the effect of the addition of persulfate on the effect of actual industrial wastewater treatment.

The embodiment adopts an electrolytic system of 60mL of actual industrial wastewater, the rotating speeds of peristaltic pumps are respectively set to be 30r/min, and the current density is set to be 40mA/cm ² The dosage of PDS is set as 10mM of single dosage. Respectively carrying out sampling analysis at 0, 5, 10, 20, 30, 60, 90 and 120min of electrolysis, wherein the detected water quality indexes comprise PDS concentration, COD concentration and nitrate concentration. The experimental results are as followsAs shown in fig. 3 and 4.

Referring to FIGS. 3 and 4, this example was conducted with the addition of "cycle + power on +10 mM PDS". Compared with the two comparative experiments, from the experimental data, the sampling analysis result of the embodiment shows that the scheme of the invention has better sewage treatment effect, lower COD residual rate and lower nitrate residual rate.

Example 5

Example 5 is to explore the influence of persulfate addition mode on the actual industrial sewage treatment effect.

The embodiment adopts an electrolytic system of 60mL of actual industrial wastewater, the rotating speeds of peristaltic pumps are respectively set to be 30r/min, and the current density is set to be 20mA/cm ² The dosage of PDS is set to be 20mM, and the adding modes are respectively set to be single adding, twice adding and four times adding. Firstly, 20mM PDS is added at one time in a single-adding experiment, and the mixture is electrified and electrolyzed; secondly, in the two-time feeding experiment, 10mMPDS is fed each time, and the feeding is respectively carried out when the reaction time is 0min and the reaction time is 60 min; and the fourth adding experiment is that 5mMPDS is added each time, and the adding is carried out when the reaction is carried out for 0min, 30min, 60min and 90min respectively. Respectively carrying out sampling analysis at 0, 5, 10, 20, 30, 60, 90 and 120min of electrolysis, wherein the detected water quality indexes comprise PDS concentration, COD concentration and nitrate concentration. The results of the experiment are shown in fig. 5 and 6. As can be seen from the experimental data, the amount of persulfate to be added depends mainly on the specific water quality conditions.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the technical scope of the present invention, so that any minor modifications, equivalent changes and modifications made to the above embodiment according to the technical spirit of the present invention are within the technical scope of the present invention.

Claims

1. A water treatment method for promoting the synchronous removal of refractory organics and nitrogen elements by using electroactive persulfate is characterized by comprising the following steps: constructing an electrolysis system with a circulating filtration flow, the electricityThe solution system is arranged at a certain distance in the order of cathode-anode-cathode; the cathode material adopts Ti/TiO ₂ -NTA/Cu-Co bifunctional electrocatalytic membrane, the bifunctional electrocatalytic membrane being made of TiO ₂ NTA as an intermediate layer, TiO ₂ -nanotube array with densely-spaced depressions on the surface of the NTA intermediate layer, TiO ₂ Forming the surface of the Cu and Co transition metal ion catalytic layer by pulse constant current electrodeposition through the NTA intermediate layer, wherein Cu and Co metal ions are simultaneously loaded on the inner wall surface of the nanotube; the anode material adopts a mesh ruthenium iridium electrode, and the cathode and the anode are respectively connected with the cathode and the anode of a direct current stabilized voltage power supply through leads; electrolyzing in a constant current mode with the current density of 20-40mA/cm ² A peristaltic pump is used as a driving force for water circulation of an electrolytic system, the peristaltic pump is set to rotate at a speed of 20-50r/min, persulfate is added to promote oxidative degradation of refractory organic matters, and the pH value of the electrolytic system is controlled to be 5-8;

the persulfate is added in a mode of selecting fractional addition, and the addition amount of PDS is set as 10mM for single addition;

the Ti/TiO ₂ the-NTA/Cu-Co bifunctional electrocatalytic membrane is prepared by the following process,

step 1, material taking: taking a piece of porous titanium base material;

step 2, high-pressure electrolysis: carrying out ultrasonic cleaning on the porous titanium substrate and then drying; the porous titanium substrate is used as an anode, and a Pt sheet is used as a cathode to be electrolyzed for 2-4 times in the prepared electrolyte at high pressure, and each time of electrolysis is 30-60 min; after the electrolysis is finished, taking out the electrode slice, cleaning and drying;

in the step 2, the porous titanium substrate is ultrasonically cleaned and dried, then the surface of the porous titanium substrate is polished by using 100-mesh sand paper, and is ultrasonically cleaned for 10min by sequentially using acetone, absolute ethyl alcohol and deionized water, the ultrasonic cleaning is repeated twice, the cleaned porous titanium substrate is placed in an electrothermal blowing drying oven and is dried at 55 ℃ to ensure the cleanness of the porous titanium substrate;

in the step 2, the prepared electrolyte comprises the following components: 97-98.5% of glycol solution, 1.25-2.75% of deionized water and 0.15-0.25% of sodium fluoride or ammonium fluoride according to weight percentage;

step 3, annealing: annealing for 1-3 h at 450-550 ℃ in a muffle furnace, naturally cooling to room temperature, taking out, cleaning and drying to obtain TiO ₂ Intermediate layer of NTA, TiO ₂ -the surface of the NTA intermediate layer is densely populated with an array of recessed nanotubes;

step 4, electrochemical deposition: TiO prepared by the above method ₂ Ti/TiO of the intermediate layer of NTA ₂ An NTA electrode is used as a cathode, a porous titanium substrate which is cleaned and dried by ultrasonic is used as an anode, the anode is placed in prepared electrodeposition liquid containing Cu and Co transition metal ions, pulse constant-current electrodeposition is carried out for 1-3 times, each time lasts for 10-20 min, and after the electrodeposition is finished, the electrode is taken out, cleaned and dried to prepare the bifunctional electrocatalysis membrane capable of efficiently activating persulfate and catalyzing nitrate reduction;

in the step 4, the electrodeposition solution containing Cu and Co transition metal ions is prepared by the method of respectively weighing a certain weight part of copper sulfate pentahydrate and cobalt sulfate heptahydrate, weighing a proper weight part of deionized water, combining and transferring the copper sulfate pentahydrate and the cobalt sulfate heptahydrate into a beaker, carrying out ultrasonic treatment for 10min, mixing uniformly, and adjusting the pH value to 4.0 by using 10% sulfuric acid, wherein the copper sulfate pentahydrate is 1 part, the cobalt sulfate heptahydrate is 1 part, and the deionized water is 100 parts by weight.

2. The method for treating water by using the electroactive persulfate as claimed in claim 1, wherein the method comprises the following steps: the cathode material adopts Ti/TiO with the diameter of 30mm, the aperture of 20 mu m and the thickness of 2mm ₂ -NTA/Cu-Co bifunctional electrocatalytic membrane.

3. The method for treating water by using the electroactive persulfate as claimed in claim 1, wherein the method comprises the following steps: the anode material adopts a reticular ruthenium-iridium electrode with the diameter of 30mm and the thickness of 1 mm.

4. The method for treating water by using the electroactive persulfate as claimed in claim 1, wherein the method comprises the following steps: when the electrolytic system is used for treating industrial wastewater, the rotating speed of the peristaltic pump is set to be 30r/min, and the current density is set to be 40mA/cm ² 。

5. The method for treating water by using the electroactive persulfate as claimed in claim 1, wherein the method comprises the following steps: persulfates are monopersulfate mixtures in which the active species is monopersulfate ion (HSO) ₅ ^— ) (ii) a Or a salt of peroxodisulfuric acid, comprising one or more mixtures of sodium, potassium and ammonium peroxodisulfate, wherein the active species is the peroxodisulfate ion (S) ₂ O ₈ ^2— ）。

6. The method for treating water by using the electroactive persulfate as claimed in claim 1, wherein the method comprises the following steps: the mechanism of promoting nitrate degradation by persulfate is as follows: persulfate obtains electrons at active sites on the surface of the electrode to generate bond breaking cracking (reactions 1 and 2), sulfate radicals generated by persulfate activation further react with water molecules to generate hydroxyl radicals, sulfate ions and hydrogen ions (reaction 3), and the hydrogen ions promote the electron reduction of nitrate on the surface of the electrode (reaction 4-6):

HSO ₅ ^— + e ^— → SO ₄ ^·— + OH ^— /HSO ₅ ^— + e ^— →SO ₄ ^2— + HO (reaction 1)

S ₂ O ₈ ^2— + e ^— → SO ₄ ^2— + SO ₄ ^·— (reaction 2)

SO ₄ ^·— +H ₂ O → HO· + H ⁺ + SO ₄ ^2— (reaction 3)

NO ₃ ^— + 2H ⁺ + 2e ^— → NO ₂ ^— + H ₂ O (reaction 4)

2NO ₃ ^— + 12H ⁺ + 10e ^— → N ₂ + 6H ₂ O (reaction 5)

NO ₃ ^— + 10H ⁺ + 8e ^— → NH ₄ ⁺ + 3H ₂ O (reaction 6).

7. The method for treating water by using the electroactive persulfate as claimed in claim 6, wherein the method comprises the following steps: the mechanism of promoting the degradation of organic matters by persulfate is as follows: hydroxyl free radicals and sulfate free radicals can be generated in the persulfate activation process, the free radicals have strong oxidizing property, and can perform chain reaction with organic matters without selectivity so as to thoroughly mineralize the organic matters:

SO ₄ ^·— + M → M ^· + SO ₄ ^2— + degradation products (reaction 7)

HO· + M → M ^· + OH ^— + degradation products (reaction 8)

M ^· + S ₂ O ₈ ^2— → SO ₄ ^·— + SO ₄ ^2— + degradation products (reaction 9)

M ^· + H ₂ O → HO· + SO ₄ ^2— + degradation products (reaction 10).

8. The method for treating water by using the electroactive persulfate as claimed in claim 1, wherein the method comprises the following steps: the electrolytic system is firstly treated at 40mA/cm before sewage degradation ² Electrolyzing the high-concentration sodium sulfate solution for 20-30min at the current density of (1), and repeating twice to activate the electrode and stabilize the electrode performance.

9. The method for treating water by using the electroactive persulfate as claimed in claim 1, wherein the method comprises the following steps: before the electrolytic system is used for degrading the sewage, firstly, a water system filter membrane with the aperture of 0.22 mu m is used for carrying out vacuum filtration on the actual industrial sewage.